1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image in a recording medium, an exposure device for exposing a photoreceptor of the image forming apparatus, and a method for operating the exposure device.
2. Description of the Related Art
A page printer executes exposure along a bus of a rotated photosensitive drum by an exposure device to form an electrostatic latent image in a peripheral surface of the photosensitive drum, adheres toner to the photosensitive drum to make the electrostatic latent image visible, and transfers an image of the photosensitive drum to paper.
In a general exposure device, a laser beam is scanned along a line by a rotated polygon lens in a dot sequential manner to form a latent image in a photosensitive drum. An exposure device in which organic electroluminescent (EL) elements are arrayed in a row is also available. The organic EL element has problems in life, emission intensity, and exposure time as compared with the other light emitting elements such as a LED. In other words, when emission intensity of the organic EL element is increased, exposure time is shortened to enable fast image forming. However, a life of the organic EL element is shortened. When emission intensity of the organic EL element is reduced, the life of the organic EL element is prolonged. However, exposure time is made longer to extend time necessary for the image forming.
Therefore, an exposure device that includes organic EL elements arrayed in a plurality of columns, and executes multiple exposure by the plurality of organic EL elements to form a pixel of one dot has been proposed (Japanese Patent Application Laid-Open Nos. 2003-341140 and 2003-341141). In other words, an image of one lines is exposed in paper by the organic EL element of a certain column, by timing when the paper is moved and the line reaches a next column, and an image of one line is exposed again to be superposed in the paper by the organic EL element of the next column, thereby forming a pixel of one dot through multiple exposure.
However, the timing when one line of the paper reaches the organic EL element of a next column from the organic EL element of a certain column and timing when the organic EL element of the next column emits a light must be synchronized with each other, and this synchronization is very difficult. Especially, a complex circuit such as a shift register for transmitting light emission data from a certain column to a next column must be mounted in the exposure device. Thus, a structure of the exposure device is complex. Further, there is a problem that the exposure device is expensive.